Cooling devices for cooling heat-generating bodies such as semiconductor elements have been conventionally known. By way of example, Japanese Patent Laying-Open No. 2004-103936 (Patent Document 1) describes a semiconductor element provided with a heat sink for dissipating heat from the semiconductor element. Here, a plurality of protruded portions are formed on an inner wall of a cover forming a cooling medium channel.
Japanese Patent Laying-Open No. 10-200278 (Patent Document 2) describes a cooling device having fins bent continuously in the shape of waves in the cooling air passing direction.
Japanese Patent Laying-Open No. 2004-119939 (Patent Document 3) describes improvement of cooling efficiency by providing a wire loop in a heat sink.
Further, Japanese Patent Laying-Open No. 2001-352025 (Patent Document 4) describes a cooling device in which flow path width is changed depending on a distance from a cooling medium inlet.
When a cooling medium is caused to flow through a cooling medium channel formed in a heat sink, boundary layer develops on a wall surface of the cooling medium channel as the flow proceeds to downstream side. Flow velocity of cooling medium decreases at the boundary layer and, therefore, development of boundary layer leads to lower cooling efficiency.
From a viewpoint of improving cooling efficiency, it may be possible to increase heat transfer area by miniaturizing the channel. If the channel is miniaturized, however, pressure loss would increase.
In ebullient cooling in which the cooling medium boils, bubble membranes form on a heat transfer surface, and the bubble membranes possibly hinder cooling by the cooling medium.
It is preferred to generate turbulence in the flow of cooling medium, in order to prevent development of boundary layer or bubble membranes described above. Patent Documents 1 to 4 mentioned above, however, do not disclose any structure that can effectively generate turbulence and improve cooling efficiency. For instance, in Patent Document 1, though protruded portions are formed on an inner surface of a case forming the cooling medium channel, the protruded portions extend along the flowing direction of cooling medium and, therefore, the protruded portions do not promote turbulence generation sufficiently to improve cooling efficiency.